This invention is an extension and improvement of our previously invented method and apparatus U.S. Pat. No. 5,951,477 for single or single repeatable absolute intracranial pressure (ICP) value measurement and diagnosing of brain pathologies based on such measurements. This document is incorporated by reference in the present application.
An apparatus for determining the pressure and flow inside the ophthalmic artery is described in U.S. Pat. No. 4,907,595 to Strauss. The apparatus uses a rigid chamber that can be affixed and sealed over the human eye so that it can be pressurized to apply an external pressure against the eyeball. An ultrasonic transducer is also mounted to the chamber and oriented to transmit ultrasonic pulses for a Doppler type measurement of the flow inside the ophthalmic artery (OA). The apparatus operates by enabling an operator to increase the pressure to such a level that the blood flow through the OA ceases. The pressure at which this occurs is then an indication of the pressure inside the OA. Typically, the pressure at which this event occurs is in the range of about 170 mmHg.
A problem associated with an apparatus as described in the '595 Patent is that the pressure necessary to obtain the desired measurement is so high that it generally exceeds maximum recommended pressures by a significant amount. When such device is then used for an extended time, tissue damage can arise and may result in an increase in the intracranial pressure, ICP, to unacceptable levels.
Another ultrasonic device for determining changes in intracranial pressure in a patient's skull is described in U.S. Pat. No. 5,117,835 to Mick. Such device involves placing a pair of ultrasonic transducers against the skull and storing received vibration signals. U.S. Pat. No. 4,984,567 to Kageyama et al. describes an apparatus for measuring ICP with an ultrasonic transducer by analyzing the acoustic reflections caused by ultrasonic pulses. Other patents related to ultrasonic measuring of either intracranial pressure or other physiological features are U.S. Pat. No. 4,204,547 to Allocca, U.S. Pat. No. 4,930,513 to Mayo et al., U.S. Pat. No. 5,016,641 to Schwartz, and U.S. Pat. No. 5,040,540 to Sackner.
None of these prior art teachings provide a clear description for obtaining a non-equivocal indication of the absolute value of intracranial pressure (aICP). The measurements tend to be obscured by noise arising from uncertainties in the measurements and by numerous influential factors, such as arterial blood pressure, cerebrovascular autoregulation state, individuality of anatomy, and patient's physiology and pathophysiology. Such influential factors cannot be eliminated by calibration of the “individual patient—non-invasive ICP meter” system because the non-invasive “golden standard” absolute ICP meter does not exist. Thus, there is a need for the capability to derive a measurement of a person's aICP in a safe, accurate and non-invasive manner that can be implemented with reasonable reliability and without the necessity for calibration.